Module collators

Stock, pure Aura collators.

This includes the basic collator, which only builds on top of the most recently included parachain block, as well as the lookahead collator, which prospectively builds on parachain blocks which have not yet been included in the relay chain.

Modules

• basic
  This provides the option to run a basic relay-chain driven Aura implementation.
• lookahead
  A collator for Aura that looks ahead of the most recently included parachain block when determining what to build upon.
• slot_based
  Architecture Overview